1. Field of the Invention
This invention relates to golf balls, and more particularly to an arrangement of dimples in the golf ball which can considerably improve flight performance.
2. Related Art Statement
In order to equally arrange dimples on the spherical surface of the golf ball as far as possible, it is generally practised to design the dimple arrangement on the basis of regular dodecahedron or regular icosahedron as disclosed in Japanese Patent laid open No. 49-52,029, British Pat. No. 377,354 and U.S. Pat. No. 4,560,168. In these conventional techniques, considering a spherical triangle obtained by projecting each of equilateral triangles constituting the regular icosahedron onto a spherical surface inscribed or circumscribed with the regular icosahedron, a great circle is formed about a line segment connecting each vertex or midpoint of the spherical triangle to a center of a sphere as a center axis, while the arrangement of dimples in the spherical triangle is determined in connection with great circles passing through the spherical triangle.
In order to enhance the aerodynamic performance of the golf ball, it is generally required to make the number of great circles as large as possible, and it is demanded that the dimple patterns are symmetrized with each other with respect to each of the great circles, whereby the lift and drag of the flying golf ball with translational and rotational motions are made substantially equal at both sides thereof with respect to the respective great circle and a probability of the golf ball rotating in the same direction as in the extending direction of the great circle. In this connection, when the great circle is depicted around a center axis connecting each vertex or midpoint of spherical pentagon or spherical triangle to the center of the sphere as in the conventional techniques, the number of great circles is 10 at maximum and it is substantially impossible to form more than 10 great circles. And also, portions of the spherical pentagon or spherical triangle divided by each great circle are not symmetrical with respect to the great circle at the position of great circle path, and hence the symmetry of dimple pattern with respect to the great circle can not be obtained. In this case, even if the golf ball flies in the extending direction of the great circle while spinning, it is subjected to different aerodynamic actions at both side portions bordering the great circle, and consequently there is a high risk of causing precession of the flying ball to result in the reduction of flying distance, the turning and the like.
For instance, this fact will be explained based on the regular icosahedron. Considering a vertex of a regular triangle t as a pole p as shown in FIG. 2, the depicted great circle corresponds to an equatorial line e, so that the phase shift of 36 degree is caused in the circumferential direction of the equatorial line e in order to make portions of the triangles t divided by the equatorial line e symmetrical. While, considering a center of regular triangle t as a pole as shown in FIG. 3, the phase shift of 60 degree is caused in the circumferential direction of the equatorial line e as a great circle. On the other hand, when considering a vertex of regular pentagon as a pole in the regular dodecahedron, the phase shift of 60 degree is also caused in the circumferential direction of the great circle. Moreover, when a center of regular pentagon is considered as a pole, the phase shift is the same as in the case of taking the vertex of the regular triangle in the regular icosahedron according to dual theory.